Aromatic dihydroxy compounds are important as various organic synthesis intermediates or raw materials, and are utilized in fields of reducing agents, rubber chemicals, dyes, medicines, agricultural chemicals, polymerization inhibitors, antioxidants, etc. On that account, improvements are always being required for processes for producing aromatic dihydroxy compounds. Examples of the aromatic dihydroxy compounds obtained by allowing a phenol compound to react with hydrogen peroxide include hydroquinone and catechol, and depending upon the production process, the product ratio between hydroquinone and catechol varies. In recent years, a process particularly for highly selectively producing hydroquinone has been eagerly desired from the viewpoint of a demand and supply balance between hydroquinone and catechol.
As processes for producing aromatic dihydroxy compounds by allowing a phenol compound to react with hydrogen peroxide, a process using an inorganic acid as a catalyst [patent literature 1], a process using a titanosilicate as a catalyst [patent literature 2], etc. are known. In these processes, however, the hydroquinone/catechol product ratio (by mol) is not more than 1.5, and a process for more highly selectively producing hydroquinone is being desired.
As methods for improving selectivity for hydroquinones, a method using a titanosilicate as a catalyst and using a cyclic ether such as dioxane as a solvent [patent literature 3], a method using an aliphatic polyether compound such as ethylene glycol dimethyl ether [patent literature 4] and a method using a polyalkylene glycol monoether compound such as polyethylene glycol mono-4-octyl phenyl ether [patent literature 5] have been developed. In these methods, however, there are problems that by-products derived from a solvent used are formed because the solvent is liable to react with hydrogen peroxide and that the yield based on hydrogen peroxide is lowered because of formation of these by-products.